HAVING been a regular reader of "The Popular Science Monthly" from its commencement, I have, of course, noticed the various articles having reference to the value of the concentric rings in determining the age of trees which from time to time have appeared in its columns, the last of which, in your August issue, induces me to give you the result of my observations upon this subject. I have had my attention directed to it during a residence of over forty years in Florida, during which my views as to the value of the rings in determining the age of trees have undergone a change. For the first few years my efforts were directed toward securing a grateful shade for the streets of the city of Jacksonville, and for this purpose the water-oak was selected on account of its beauty, symmetry of form, and rapid growth. And now the appellation of "Forest City," applied to it by visitors, is in no sense inappropriate, for many of the older trees have attained a size which in the State of New York, whence I came, would have required a hundred years to reach. Strangers from the North are apt to overestimate the age of our trees, and the number of rings presented appears to confirm in many instances the correctness of their estimate. When first called upon to account for the discrepancy shown by the rings, and the known age of the tree, I was perplexed and at a loss to find a satisfactory solution of the problem. But, having from my first arrival here kept a careful record of the weather, an analysis of my tables, a comparison with the record made by Nature on her infallible tablets in the trees furnished me the key to it.

Here, as well as at the North, the cold of winter puts a stop to vegetable growth, and in all exogenous trees a concentric ring will be formed, embracing all woody matter deposited since the preceding stop to its growth; but here in this climate causes are in operation that frequently produce as complete a stop to vegetable growth as docs the cold of winter.

Our spring begins in February, when growth commences a new deposit between the bark and wood, but often (not always) there comes so severe a drought during late spring and early summer as to produce as full and complete a stop to vegetable growth as does the cold of winter; immediately after comes on our rainy season, generally

about the middle or last of June, producing a rapid and luxuriant growth, which continues until winter again puts a stop to it. Our rainy seasons, however, do not consist of deluges of rain that overflood the country, but of daily showers, occurring in the early part of the afternoon, lasting an hour or two, leaving the sky bright and clear, the air cool for the rest of the twenty-four hours, comfortable to man, and favorable to luxuriant vegetable growth. The rainy seasons, when regular, continue day after day, for about sixty days, but often there is an interval of clear, sunshiny weather, for about a fortnight, between the rainy periods, which carries the rainy season into the fall months. Upon examination of the tree, it will be found that, when those severe droughts have put a stop to vegetable growth, a concentric ring well defined has been produced, and the growth which has occurred during the rainy season and until winter's cold has formed another and perhaps a thicker ring, making two rings in one year. But the phenomena of such a year are not necessarily repeated each year, for considerable variation occurs.

What physiological meaning is attached to these rings? They simply mark the amount of growth of woody matter deposited day by day between the periods when a stop to vegetable growth has prevented daily deposit and produced a line of demarkation, whether from drought of summer or cold of winter.

For some two or three years before his lamented death, Professor Jeffries Wyman was exploring the mounds of Florida. It was my privilege to enjoy his acquaintance and learn his views on matters of science in which we were both interested. I have heard him express his belief that he had reached an approximate age of some of the mounds which he had explored, by the indications which the trees growing upon them had furnished. It so happened that we were one time walking down-town together and passed a lot where preparations for building a dwelling-house were going on, and a tree which stood upon the proposed site was being cut down. He remarked that it was sacrilege to cut down so noble a tree; he would have changed the site of the house and let the tree remain as a shade, "for," said he, "it would take a hundred years to produce such another tree." In that, I told him, he was mistaken, as I knew the age of that tree, and it was not yet thirty years old. "Impossible!" said he, and proposed, as the tree had been felled and lay on the ground, to go over and count the rings, to which I assented, and looked on while the professor undertook the task. I soon saw that he was under considerable perplexity. He said he found it no easy matter, as some of the rings were so indistinct that he was unable to decide whether they were single or double, "but," said he, "I can make out thirty or more, but how many more I will not venture to say." I carefully examined the rings, and saw what I had seen before. I have no doubt that at least forty rings could have been identified by a close and critical examination. I reiterated my statement as to the real age of the tree, for thirty years before I had seen corn growing on this spot.

I told him the tree which he had just examined presented a true record of the weather, so far as drought and rainfall were concerned, since it had been a tree, and invited him to call at my office and examine the records which I had kept during the same period, and he would find a confirmation of what I had stated. "This theory," says he, "is new to me, but it is plausible, and the facts here presented seem to substantiate it." His death, after his return North that year, put a stop to further scientific investigations in Florida on his part, but the reasons then given have induced many others to change their views as to the value of concentric rings in determining the age of trees. In a climate like that of Florida they certainly are not to be depended on; how it may be in a more northern latitude I will not undertake to assert or deny, but it seems to me probable that any arrest of growth, from climatic or other causes, will be indicated by some peculiarity in the formation of the concentric rings of the tree; and it may in some instances present two rings instead of one to mark an entire year's growth.

Very respectfully,

A. S. Baldwin, M. D.

Jacksonville, Fla.,September 27, 1SS3.

BIRTH-RATE IN A NEW HAMPSHIRE TOWN.

Messrs. Editors:

While preparing a history of Chesterfield, Cheshire County, New Hampshire, the writer has had occasion to collect the birthrecords of several hundred families, including both original settlers and their descendants. These families may be regarded as typical New England families, the original settlers having come, for the most part, from Massachusetts, Connecticut, and Rhode Island. The foreign element has always been very small in the town. A careful inspection of the birth-records in question (taking into account the children of one marriage only, in cases in which the father married more than once, and excluding the still-born) yields the following results:

1. The total number of births in 165 families, from 1750 to 1810, was 1,359, or an average number of 813/55 to each family.

2. The total number of births in 328 families, from 1810 to 1870, was 1,825, or an average number of 5185/328to each family.

3. The average number of births in 140 families, from 1810 to 1840, was 642/70.

These figures show that there was a marked decrease in the birth-rate of Chesterfield families between 1810 and 1840, and that in the period of sixty years, from 1810 to 1870, this decrease was still more marked.

If what is true of this town, in this respect, is also true of the majority of New England towns, as is quite probable, it would appear that the birth-rate in New England families has steadily decreased since the introduction of railroads and the extensive establishment of manufactories.

O. E. Randall.

West Chesterfield, N. H.,September 3, 1833.

"TIDAL ANOMALIES."

Messrs. Editors:

In the January number of your journal there is a communication under the above-Named title, from G. W. Grim, of the bark Coryphene. Referring to a preceding letter of mine, he says of my article, " After demonstrating, as a result of Professor Schneider's theory, a great inequality in the daily range of the tides," etc.

The gentleman entirely misconceives the purport of my criticism. I showed that Professor Schneider's theory is demonstrably false, and my reference to the New York tides was merely to show by them that the theory does not conform to the facts. The "daily inequality" is easy to explain: most of those given by Mr. Grim present no difficulty at all—with others, when the facts are established, the explanation will follow.

No theory of the tides is of any value except as based on facts—in which respect Mr. Grim's theory is worse off than Mr. Schneider's. A theory of the tides resting solely on one's inner consciousness is not a valuable contribution to knowledge.

R. W. McFarland.

Ohio State University,December 27, 1883.

CARRYING-POWER OF FLUID CURRENTS.

Messrs. Editors:

I see that in your November number, page 95, Mr. Carter applies the "law of carrying-power of currents" (R ɑ v6) to blood-currents carrying waste matter. Now, I make no objection to the general correctness of Mr. Carter's conclusions, but I am sure that this is an entire misapplication of the law.

The fact is, this law is so often misunderstood and misapplied that it becomes dangerous to use it without clear conceptions of its nature. By many good hydraulic engineers it has been confounded with the law of erosive power of currents; by others, with the quantity of material carried in suspension; and now Mr. Carter confounds it with quantity of matter carried in solution. It were well if, in popular language, the name of the law were changed. Perhaps it would be less liable to be misunderstood if it were called "lifting-power of currents." It expresses only the size of the largest transportable particle. It is a law which concerns mainly the geologist and the ore-dresser. The geologist finds certain bowlders scattered about in the lower part of a valley. The question is, Were they brought by currents; and, if so, what was the velocity? It is applied thus, by Dana, in discussing the material brought down by the Connecticut River during the Champlain epoch. Again, the ore-dresser has crushed rock, which he wishes to sort by means of a current decreasing in velocity in its course. The question is, Where will the particles of different sizes drop? I do not know any other cases of practical application. Certainly it can have no application to matters in solution.